(a) Field of the Invention
The present invention concerns internal Combustion engines and, more particularly, a gaseous fuel injection system for same utilizing mechanical and pneumatic means.
(b) The Prior Art
Internal combustion engines that operate on gaseous fuel only or alternately on liquid fuel are long and well-known. Typical such fuel systems employ a negative or less than ambient atmospheric pressure to, in effect, suck the gaseous fuel from a zero pressure governor. Usually the negative pressure is created by a venturi and the gaseous fuel enters the throat of the venturi from the zero pressure governor in amounts proportional to the decreases in the ambient pressure at the throat of the venturi which, in turn, is proportional to the rate of air flow through the venturi itself. In these systems, thus, the pressure of the gaseous fuel entering the engine's air intake system is always less than that of the ambient atmosphere. When a supercharger is also used, the foregoing is still true if "ambient" is considered to be the air pressure at the inlet of the engine's carburetion system, assuming the supercharger is upstream of the latter.
The venturis used in the foregoing systems are relatively large in diameter in order to minimize pressure loss, since the length of the typical venturi employed, such as that in a carburetor, is relatively short and therefore pressure recovery is not the best. The relatively large venturi diameter, however, impairs the strength of the "signal", as it were, transmitted to the zero pressure governor, especially at lower air speeds through the venturi, and so impairs control over the air-to-fuel ratio. Unlike the situation in the case of liquid fuels it is not possible to increase the strength of that "signal" by the use of a secondary or booster venturi within the main venturi in the case of gaseous fuels. This is because the gaseous fuel in conventional systems is introduced at the very point where the "signal" is taken, namely, the throat of the venturi, and unlike the situation with liquid fuels, a booster venturi is too small to be able to introduce enough gaseous fuel into the air to provide a proper air-to-fuel ratio (about one part fuel to fifteen parts air by weight in the case of hydrocarbon fuels) in view not only of the quantity of air through the booster venturi itself but also in view of the physical size needed to conduct fuel in the gaseous state in sufficient quantities.
The foregoing difficulties persist whether the engine is to operate on gaseous fuel alone or alternately on liquid fuel. In latter instances sometimes the venturi of the liquid fuel carburetor is used to introduce the gaseous fuel, or a separate venturi immediately upstream of the liquid fuel venturi is employed for the gaseous fuel, as in U.S. Pat. No. 4,375,798, for instance. Yet in both these cases the gaseous fuel is still introduced at the very point from which the "signal" to the zero pressure governor is generated and thus at a pressure less than that of the ambient atmosphere. The same is true in a liquid fuel injection system where an alternate gaseous fuel system uses a venturi to measure and introduce the gaseous fuel, as mentioned in the foregoing patent. If, in order to employ a longer venturi for better pressure recovery, which in turn allows a smaller venturi diameter for better fuel metering, that is, a better "signal", the venturi for gaseous fuel is placed in an air intake trunk well upstream of the liquid fuel carburetor, or in an alternate intake trunk in the case of a liquid fuel injection system, a safety hazard arises in the case of an engine backfire since the entire air trunk downstream of the venturi is filled with a combustible mixture of air and fuel.
So the chief object of the present invention is the provision of a gaseous fuel system for internal combustion engines which avoid the deficiencies and hazards mentioned.
Another object is to do so in a manner which is readily adapted to either liquid fuel carbureted or injected systems having a wide variety of air induction shapes and designs.
A further object is to accomplish the foregoing with relatively little complexity and at relatively small cost.